A PPPoE authentication technology is a common broadband authentication technology, and by means of the PPPoE authentication technology, a user terminal can access a broadband access server (BAS) corresponding to an operator.
A PPPoE authentication process includes two stages. At a first stage, that is, a discovery stage, a user terminal discovers BASs supporting the PPPoE in a broadcast domain in which the user terminal is located, and selects a BAS from the BASs to establish a session. During specific implementation, the user terminal sends a PPPoE active discovery initiation (PADI) packet to the broadcast domain in a broadcast manner, and any BAS supporting the PPPoE returns a PPPoE active discovery offer (PADO) packet to the user terminal after receiving the PADI packet. The user terminal receives multiple PADO packets and selects, according to a particular rule, a BAS corresponding to a PADO packet to establish a session. A second stage is a session stage. At this stage, the user terminal sends authentication information to the BAS that establishes the session with the user terminal, so as to perform authentication.
However, if multiple BASs corresponding to multiple operators exist in the broadcast domain in which the user terminal is located, and all the multiple BASs support the PPPoE, when selecting a corresponding BAS according to the received multiple PADO packets, the user terminal probably selects an incorrect BAS to establish a session. Subsequently, authentication inevitably fails, leading to a problem that the user terminal cannot perform access. For example, both a BAS corresponding to a telecommunications network and a BAS corresponding to an education network exist in a broadcast domain in which a user terminal is located. The user terminal can access the telecommunications network according to authentication information. At the discovery stage, the user terminal separately sends PADI packets to the BAS corresponding to the telecommunications network and the BAS corresponding to the education network, and separately receives returned PADO packets. The user terminal establishes, according to the received PADO packet, a session with the BAS corresponding to the education network. At the session stage, when the user terminal sends, to the BAS corresponding to the education network, authentication information for accessing the telecommunications network, authentication inevitably fails. In addition, the user terminal cannot access the BAS corresponding to the telecommunications network. As can be seen, the user terminal establishes the session with the incorrect BAS, leading to the problem that the user terminal cannot perform access.